Patent GB-1207191-A (GB)
Title: Angle encoding
IPC: G08C19/46
Filed: 1967-10-04
Abstract: 1,207,191. Encoders; generating trigonometrical functions. TOWSON LABORATORIES Inc. 4 Oct., 1967 [21 Oct., 1966], No. 45285/67. Headings G4G and G4H. From signals sin # and cos # representing for example the angle of rotation # of a resolver shaft, signals K sin (0 - #) and K cos (0 - #) are derived. The apparatus is used to give a digital indication of the angle # by determining the amount of rotation # necessary to zeroize sine (# - #). Inputs sin #, cos # at terminals 26, 28 (Fig. 2), are fed to operational amplifiers 30, 34 feeding signals - sin #, -cos # to further operational amplifiers 32, 36 to which are also fed via resistances 34, 48 of resistance cos # and - sin # respectively so that outputs proportional to (sin # - tan # cos #), (cos #, + tan # sin #), i.e. sin (# - #), cos (# - #) are obtained on leads 22, 24. Fig. 3 shows an embodiment suitable for rotating sine # and cos # in discrete steps of #. If the charge on capacitors Cox, Coy is initially such as to produce output signals sin #, cos # when a switch S1 is operated capacitors Cax, Cay are charged to Cax cos # and - Cay sin #. Subsequent operation of switch S2 transfers these charges to storage amplifiers 50, 52 to give outputs of the form (sin # - tan # cos #) (cos # + tan # sin #) where tan # Each subsequent operation of the switches rotates # through an angle # and by counting the number of operations necessary to reduce the output on lead 58 to zero the angle # may be measured. In the encoder of Fig. 4 when measuring the angle of rotation of a resolver 101, the excitation voltage 103 controls a programmer 162. Initially gate 200 is enabled by signals #A, B to feed the sin # resolver output to a comparator 166. Dependent on the polarity of sin # a pulse appears at either output 184 or 186. In accordance with this polarity the comparator is then connected by a gate 202 or a gate 204 to the cos # or - cos # signal and a pulse is delivered in accordance with the polarity of the cosine signal. Gates 176, 182 are enabled at this time so that either switch S3 (for positive cos #) or S4 (for negative cos #) are operated, followed by switch S2 to rotate # either clockwise or counterclockwise by 45 degrees. The polarity of the cosine of this angle is then determined and the switches S3 or S4 operated again to rotate # by 22¢ degrees. The rotations are reduced by two during each bit time by the programmer sequentially operating switches S5 to S13 in capacitance attenuator networks 140, 142. The binary coded output signal may be taken from either output lead 184 or 186. In a modification (Fig. 9, not shown) using a signal modifier similar to that of Fig. 2, pairs of ganged switches (S -A , S -B , S +A , S +B ) are provided the S_ switches when operated providing a rotation of minus # and the S +  switches rotation of plus #. A plurality of such modifying stages are connected in cascade the switches in each stage being controlled by the polarity of the input sine #, the output bits from each stage also depending on this polarity. The rotations # for the stages are in decreasing binary weight, i.e. radians. In a further modification (Fig. 12, not shown), each stage of the cascade encoder produces a change of + # and additionally of #.